'''Chicago''' ( or ), officially the '''City of Chicago''', is the List of United States cities by population|third-most populous city
in the United States
. With over 2.7 million residents, it is the most populous city in the state of Illinois
, and the Midwestern United States
. It is the county seat
of Cook County, Illinois|Cook County
. The Chicago metropolitan area
, often referred to as Chicagoland, has nearly 10 million people and is the third-largest in the U.S.
Chicago was incorporated as a city in 1837, near a Chicago Portage|portage
between the Great Lakes
and the Mississippi watershed|Mississippi River watershed
, and grew rapidly in the mid-nineteenth century.
Positioned along Lake Michigan
, the city is an international hub for finance, commerce, industry, technology, telecommunications, and transportation: O'Hare International Airport